Bump pytest-mock from 3.3.1 to 3.4.0 (#270)

Bumps [pytest-mock](https://github.com/pytest-dev/pytest-mock) from 3.3.1 to 3.4.0.
- [Release notes](https://github.com/pytest-dev/pytest-mock/releases)
- [Changelog](https://github.com/pytest-dev/pytest-mock/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-mock@v3.3.1...v3.4.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Dylan Anthony <[email protected]>

Author: dependabot[bot]